Many versions of such claw pole generators are known which provide alternating current output and are referred to as alternators; the so-called magnetic coupling rotor generators, to which the invention relates in particular, represent a special type of claw pole generators, in which only the claw poles rotate, while the excitation winding and annular magnetic flux guide elements remains stationary. In a known magnetic coupling rotor generator of this type (Bosch Automotive Handbook, published by Robert Bosch GmbH, Stuttgart, Sept. 1986, pp. 430-431), generator is described in which the excitation winding is supplied with current directly by the rectifier via the regulator, since because of the stationary excitation winding, sliprings and slip-ring contacts are not required. This gives the generator a longer service life but has the disadvantage of greater weight by comparison with claw pole generators of equal power, because the magnetic flux has to bridge two further air gaps in addition to the working air gap. Besides the increased weight, the structural length is greater and the excitation requirement higher, at comparable power; or if the magnetic coupling rotor generators have the same dimensions as other claw pole generators, then less power is produced. In experimental attempts at shortening the structural length in known magnetic coupling rotor generators by shortening the additional air gaps, there was an even higher requirement for excitation current, yet no success at actually overcoming the problem.